Simulation of Ultrasonic Fields and Echo Signals using Cross-Section Photograph of Test Object and FDTD Method

We present a simulation technique of ultrasonic fields and echo signals, that uses a digitized crosssection photograph of a test object and a digitized cross-section figure of an ultrasonic probe as input data. The input data file is referred to as a shape file. In the shape file, different colors are assigned to different materials, for example, red for a piezoelectric transducer, green for the wedge of a probe, and blue for a test object, for the purpose of distinguishing between the different materials. Each color contains information on material parameters, such as the velocity of a longitudinal wave in the material, that of a shear wave, and the material density. Using the shape file, ultrasonic transmitted fields, scattered fields, and echo signals are calculated by a two-dimensional elastic finite-difference time domain (FDTD) method. The pixel size of the shape file is set to be the same as the grid size used in the FDTD simulation. A simulation result using real photographs of butt weld joints is